The present invention generally relates to microelectronic devices. More particularly, the invention relates to programmable microelectronic structures suitable for use in integrated circuits.
Memory devices are often used in electronic systems and computers to store information in the form of binary data. These memory devices may be characterized into various types, each type having associated with it various advantages and disadvantages.
For example, random access memory (xe2x80x9cRAMxe2x80x9d) which may be found in personal computers is volatile semiconductor memory; in other words, the stored data is lost if the power source is disconnected or removed. Dynamic RAM (xe2x80x9cDRAMxe2x80x9d) is particularly volatile in that it must be xe2x80x9crefreshedxe2x80x9d (i.e., recharged) every few microseconds in order to maintain the stored data. Static RAM (xe2x80x9cSRAMxe2x80x9d) will hold the data after one writing so long as the power source is maintained; once the power source is disconnected, however, the data is lost. Thus, in these volatile memory configurations, information is only retained so long as the power to the system is not turned off In general, these RAM devices may be expensive to manufacture and consume relatively large amounts of energy during operation of the devices. Accordingly, improved memory devices suitable for use in personal computers and the like are desirable.
CD-ROM and DVD-ROM are examples of non-volatile memory. DVD-ROM is large enough to contain lengthy audio and video information segments; however, information can only be read from and not written to this memory. Thus, once a DVD-ROM is programmed during manufacture, it cannot be reprogrammed with new information.
Other storage devices such as magnetic storage devices (e.g., floppy disks, hard disks and magnetic tape) as well as other systems, such as optical disks, are non-volatile, have extremely high capacity, and can be rewritten many times. Unfortunately, these memory devices are physically large, are shock/vibration-sensitive, require expensive mechanical drives, and may consume relatively large amounts of power. These negative aspects make these memory devices non-ideal for low power portable applications such as lap-top and palm-top computers, personal digital assistants (xe2x80x9cPDAsxe2x80x9d), and the like.
Due, at least in part, to a rapidly growing numbers of compact, low-power portable computer systems in which stored information changes regularly, read/write semiconductor memories have become increasingly desirable and widespread. Furthermore, because these portable systems often require data storage when the power is turned off, non-volatile storage device are desired for use in such systems.
One type of programmable semiconductor non-volatile memory device suitable for use in such systems is a programmable read-only memory (xe2x80x9cPROMxe2x80x9d) device. One type of PROM, a write-once read-many (xe2x80x9cWORMxe2x80x9d) device, uses an array of fusible links. Once programmed, the WORM device cannot be reprogrammed.
Other forms of PROM devices include erasable PROM (xe2x80x9cEPROMxe2x80x9d) and electrically erasable PROM (EEPROM) devices, which are alterable after an initial programming. EPROM devices generally require an erase step involving exposure to ultra violet light prior to programming the device. Thus, such devices are generally not well suited for use in portable electronic devices. EEPROM devices are generally easier to program, but suffer from other deficiencies. In particular, EEPROM devices are relatively complex, are relatively difficult to manufacture, and are relatively large. Furthermore, a circuit including EEPROM devices must withstand the high voltages necessary to program the device. Consequently, EEPROM cost per bit of memory capacity is extremely high compared with other means of data storage. Another disadvantage of EEPROM devices is that although they can retain data without having the power source connected, they require relatively large amounts of power to program. This power drain can be considerable in a compact portable system powered by a battery.
In view of the various problems associated with conventional data storage devices described above, a relatively non-volatile, programmable device which is relatively simple and inexpensive to produce is desired. Furthermore, this memory technology should meet the requirements of the new generation of portable computer devices by operating at a relatively low voltage while providing high storage density, and a low manufacturing cost.
The present invention provides improved microelectronic devices for use in integrated circuits. More particularly, the invention provides relatively non-volatile, programmable devices suitable for memory and other integrated circuits.
The ways in which the present invention addresses various drawbacks of now-known programmable devices are discussed in greater detail below. However, in general, the present invention provides a programmable device that is relatively easy and inexpensive to manufacture, and which is relatively easy to program.
In accordance with one exemplary embodiment of the present invention, a programmable structure includes an ion conductor and at least two electrodes. The structure is configured such that when a bias is applied across two electrodes, one or more electrical properties of the structure change. In accordance with one aspect of this embodiment, a resistance across the structure changes when a bias is applied across the electrodes. In accordance with other aspects of this embodiment, a capacitance, or other electrical properties of the structure change upon application of a bias across the electrodes. One or more of these electrical changes may suitably be detected. Thus, stored information may be retrieved from a circuit including the structure.
In accordance with another exemplary embodiment of the invention, a programmable structure includes an ion conductor, at least two electrodes, and a barrier interposed between at least a portion of one of the electrodes and the ion conductor. In accordance with one aspect of this embodiment the barrier material includes a material configured to reduce diffusion of ions between the ion conductor and at least one electrode. The diffusion barrier may also serve to prevent undesired electrodeposit growth within a portion of the structure. In accordance with another aspect, the barrier material includes an insulating material. Inclusion of an insulating material increases the voltage required to reduce the resistance of the device to its lowest possible value. Devices including an insulating barrier may be well suited for non-volatile memory (e.g., EEPROM) applications.
In accordance with another exemplary embodiment of the invention, a programmable microelectronic structure is formed on a surface of a substrate by forming a first electrode on the substrate, depositing a layer of ion conductor material over the first electrode, and depositing conductive material onto the ion conductor material. In accordance with one aspect of this embodiment, a solid solution including the ion conductor and excess conductive material is formed by dissolving (e.g., via thermal or photodissolution) a portion of the conductive material in the ion conductor. In accordance with a further aspect, only a portion of the conductive material is dissolved, such that a portion of the conductive material remains on a surface of the ion conductor to form an electrode on a surface of the ion conductor material.
In accordance with another embodiment of the present invention, at least a portion of a programmable structure is formed within a through-hole or via in an insulating material. In accordance with one aspect of this embodiment, a first electrode feature is formed on a surface of a substrate, insulating material is deposited onto a surface of the electrode feature, a via is formed within the insulating material, and a portion of the programmable structure is formed within the via. In accordance with one aspect of this embodiment, after the via is formed within the insulating material, a portion of the structure within the via is formed by depositing an ion conductive material onto the conductive material, depositing a second electrode material onto the ion conductive material, and, if desired, removing any excess electrode, ion conductor, and/or insulating material.
In accordance with a further exemplary embodiment of the invention, multiple bits of information are stored in a single programmable structure.
In accordance with yet another exemplary embodiment of the present invention, a capacitance of a programmable structure is altered by causing ions within an ion conductor of the structure to migrate.